Enterotoxigenic Escherichia coli (ETEC) are an important cause of travelers' and infantile diarrhea worldwide particularly in underdeveloped and/or tropical countries. The major thrust of this proposal is to investigate one of the major virulence factors of ETEC, colonization factor antigen (CFA)/I, a plasmid mediated adherence fimbria found on certain of ETEC. CFA/I plasmids have been examined for the possibility of other associated phenotypic markers including antibiotic resistance, production of heat stable or heat labile toxin, fermentation of carbonhydrates, production of colicin and of and of hemolysin and by molecular weight determinations. These plasmlids will be will further characterized by agarose gel electrophoresis os restriction endonuclease digestion fragments and by hybridization of pTx, a CFA/I:ST plasmid transferred from a strain isolated during a nonsocomial outbreak of diarrhea. In addition, the ability of different bacteria to express CFA/I and the stability of pTx in different strains is being investigated. Finally, cloning of CFA/I subunit and of CFA/I fimbria will be done using restriction endonuclease cleavage fragments of a CFA/I plasmid, which are then ligated into appropriate cloning vectors and transformed into an E. coli K12 which has been shown to be able to express CFA/I. The DNA segments(s) necessary for synthesis of the fimbriae will be determined by transposon insertion-deletion interruption of CFA/I production. The immediate goals of this proposal are to delineate the homogeneity or heterogeneity of CFA/I plasmids, to clone the CFA/I gene(s) using hosts which are capable of CFA/I expression, and to develop a sensitive and specific DNA probe using this clone. The long range goal (for future studies) will be to use this CFA/I probe in field studies in order to define the true epidemiology of CFA/I as it relates to ETEC. Such a strain also has potential as a live vaccine strain but the worldwide prevalence of this fimbrial antigen should first be established.